1. Field of the Invention
The present invention relates to a particulate matter washing apparatus or method for washing contaminated particulate matter scraped up from filtering media in a filtering pond or from a bottom of a waste water pond or a sedimentation basin, etc., or surface-covering sand to remove muck on or materials covering the surface of the grains of the particulate matter.
2. Description of the Prior Art
Filtering sand used in a water purifying plant is collected from a river bottom or a river-mouth, but a quantity of the resource is limited, so that sand once used is again used after cleaning or other similar processing. In association with rapid contamination of resource water or under influence caused by contaminants flowing into a filtering pond, such phenomena have been observed as that a grain diameter of the filtering material has become larger due to deposition of sludge or that sludge is separated from the filtering media when a grain diameter of filtering media becomes larger as described above, a space between the filtering media is reduced and the filtering efficiency becomes lower. So it is required to periodically take out the filtering media from the filtering pond and remove muck from a surface of the filtering media by means of washing.
Conventionally, in the processing for washing filtering media, generally there has been used a washing apparatus having agitation vanes to mix contaminated sand and cleaning water and agitate the mixture, but when a large quantity of contaminated sand is forcefully agitated, the sand grains are pulverized due to collision with the agitation vanes or friction between the filtering media themselves, and resultantly a portion which can not be recycled increases, and further if a quantity of cleaning water is small, the separated contaminants are again deposited on the sand grains, which makes it difficult for us to expect high efficiency in the processing for cleaning.
Also as the so-called washing apparatus for sand, there has been proposed an apparatus having a sand scrape-up section at a central position of the basic body for agitating and washing sand by making use of rotation of a screw conveyor provided in the sand scrape-up section. This sand washing apparatus is an apparatus used mainly for removing salt deposited on a surface of sea sand, and has the construction in which the screw conveyor has sand scrape-up vanes in its lower section and also agitation vanes on its upper section and blades for distribution are provided in the upper section of the sand scrape-up section.
In this type of sand washing apparatus as described above, sand put in a cleaning tank is raised due to effect by sand scrape-up vanes up to the agitation vane section, where the sand is mixed with cleaning water poured thereinto, the sand in the cleaning water is agitated, diluted, washed, and further raised upward by making use of rotation of agitation vanes, and then the sand is homogenized and forcefully moved from the sand scrape-up section to the cleaning tank. Because of this construction, it is required to inject sand into the cleaning tank up to at least a height of the blades for distribution, and further the cleaning water is supplied at a section where the agitation vanes rotate and salty water after cleaning is overflown from a water discharge pipe provided in the upper section of the cleaning tank, so that the cleaning tank is always required to be filled with the cleaning water.
As described above, generally the conventional type of sand washing apparatus has the configuration in which sea sand filling a tank is floated in and agitated with cleaning water to make salt deposited on a surface of sand grain dissolved in the cleaning water to acquire cleaned sand.
Even if filtering media is washed by using the conventional type of sand washing apparatus as described above, however, contaminants deposited on a gain surface are, different from salt, not dissolved into cleaning water, so that it has been impossible to expect a high cleaning effect. Also, when a supply rate of cleaning water is lowered to suppress floating of sand to be cleaned, as a large quantity of contaminated sand is forcefully agitated by the agitation vanes, which sometimes causes breakage pulverization of sand gains. Also as the sand scrape-up vanes and agitation vanes continue to rotate in the sand, so that friction between the agitation vanes and sand is disadvantageously large.
It is an object of the present invention to provide a sand washing apparatus which can effectively remove contaminants despited on and covering a surface of sand gain without pulverizing the injected sand and also in which wearing is generated little in the agitation member.
To solve the problems as described above, the present invention provides a method of washing contaminated particulate matter comprising:
providing a cleaning tank, for storing the contaminated particulate matter and cleaning water, in which the contaminated particulate matter and the cleaning water are contained in their respective predetermined amounts and in which a screw conveyor is disposed for rotation around a substantially vertical axis so that the lower part of the screw conveyor is positioned under the surface of the cleaning water contained in the cleaning tank and the upper part of the screw conveyor is positioned above the surface of the cleaning water in the cleaning tank;
contacting, under the surface of the water, the grains of the particulate matter with each other with sludge, which comes from the contaminated particulate matter and is present in the water, being interposed therebetween to remove at least a part of contamination substances from the surface of the grains of the particulate matter and to wash off the substances into the water, while raising the particulate matter and the water by means of the rotation of the screw conveyor under the surface of the water;
fluidizing, above the surface of the water, the particulate matter on the surface of the screw conveyor and thereby contacting the grains of the particulate matter with each other with a slight amount of the water including the sludge being interposed therebetween to remove at least a part of the remaining contamination substances from the surface of the grains of the particulate matter; and
allowing the particulate matter, which has been raised, to fall down to the lower part of the screw conveyor through a way outside the screw conveyor;
whereby the contaminated particulate matter is cleaned off by way of repeating the raising and falling.
When the particulate mater is allowed to fall down, it is preferable to drop the particulate matter onto the surface of the water in the cleaning tank in order to avoid collision of the grains of the particulate matter with each other so that the grains of the particulate matter can be prevented from breaking or smashing into pieces.
It is preferable that the cleaning water is not replaced until the washing of the particulate mater is completed, but a part of the water may be replaced with unused water during the washing of the particulate matter. The presence of the sludge in the cleaning water provides better results in washing the particulate matter.
The surface of the water in the cleaning tank is preferably maintained at a height ranging from xc2xd to ⅔ of the height of the screw conveyor. The weight ratio of the particulate matter to the water in the cleaning tank may be set to be between 1.0:1 and 4.5:1 if it is desired. The screw conveyor is preferably rotated at a speed such that the water can be raised to the top of the screw conveyor.
Examples of the particulate matter as used herein include sand, particles of various kinds of minerals including zeolite, ion-exchange resins, scraps or debris of plastics or metals, such as those for recycling use, fine copper particles or powder obtained from etching waste liquid, and any other particulate substances.
The present invention also provides a particulate matter washing apparatus comprising:
a cleaning tank for storing particulate matter and cleaning water;
a screw conveyor with a cylindrical wall surrounding the conveyor, said screw conveyor being adapted for rotation around a substantially vertical axis in the cleaning tank;
a rotation mechanism for rotating the screw conveyor at a speed so that the particulate matter and the water are raised, in the lower part of the screw conveyor under the surface of the water, by means of the rotation of the screw conveyor, whereby at least a part of contamination substances on the particulate matter are removed by the contact between the grains of the particulate matter with the cleaning water being interposed therebetween, and so that the particulate matter is fluidized on the surface of the screw conveyor in the upper part of the screw conveyor above the surface of the water to remove at least a part of the remaining contamination substances from the particulate matter by means of the contact between the grains of the particulate matter; and
a particulate matter circulating mechanism in which the particulate matter that has been raised is allowed to fall down to the lower part of the screw conveyor through a way outside the screw conveyor and is allowed to be raised again by the screw conveyor.
A gap between the outside periphery of the screw conveyor and the cylindrical wall surrounding the screw conveyor is preferably not less than three times as large as the particle size of the grains of the particulate matter.
In one embodiment of the present invention, the side wall of the cleaning tank constitutes the cylindrical wall surrounding the screw conveyor, and a circulating path making up the particulate matter circulating mechanism is provided outside the side wall, as shown in FIG. 6.
In another embodiment of the present invention, the side wall of the cleaning tank constitutes the cylindrical wall surrounding the screw conveyor, and a circulating path making up the particulate matter circulating mechanism is provided inside the side wall, as shown in FIG. 7.
A plurality of relatively small vanes may be provided substantially in parallel with, and between, adjacent relatively large vanes of the screw conveyor. The relatively small vanes are preferably wing-shaped. It is also preferable that the relatively small vanes are fixed to supporting bars which are provided in erect posture on the relatively larger vanes of the screw conveyor. It is further preferable that the cross-section of the supporting bars is wing-shaped with being thinner toward the direction of rotation of the screw conveyor.
In another aspect of the present invention, the particulate matter washing apparatus comprises a cleaning tank having a sand inlet port in its upper section and a sand outlet port in its lower section for storing therein sand and cleaning water; an agitation tank provided in the erected posture and having openings in its upper and lower edge sections; and a screw conveyor rotating in this agitation tank, and the screw conveyor projects from a top surface of a layer of sand deposited within the agitation tank as well as form a top surface of the cleaning water, and has a fluidized sand up-flow section for flowing the fluidized sand to be washed up to the upper opening section of the agitation tank.
Quantities of sand and cleaning water to be injected into the cleaning tank are set to levels so that an upper half of the screw conveyor projects from the sand and water within the agitation tank. When the screw conveyor is rotated, the sand and cleaning water gradually supplied from the lower opening section of the agitation tank goes up along the spiral vane. Then, by setting rpm of the screw conveyor to a high value so that the sand and water stored in the tank can go up to an upper edge of the vane, fluidization of the sand can be realized, and in this state sand gains collide to and scrub each other in the up-flowing water. It is necessary to set the rotational speed so that the fluidized sand is discharged from the agitation tank into the cleaning tank.
Deposited sand and cleaning water there are pushed up in the state where they are restricted by the screw conveyor, so that their free movement is suppressed, but in the fluidized sand up-flow section there is no restriction by the screw conveyor, so that cleaning water continues to flow upward actively moving. Then the fluidized sand forms a discontinuous eddy flow and generates friction between sand grains, thus the washing effect being achieved.
A quantity of water dropped from a clearance between an external edge section of the screw conveyor and an internal wall of the agitation tank is larger than that of the sand, so that a density of sand becomes higher, as it goes to a higher section of the screw, as compared to that when it is deposited on the bottom of the agitation tank. Namely the chance for sand grains to scrub each other in the fluidized sand on the conveyor projecting from a layer of deposited sand becomes higher than that in sand agitated together with water in the deposited section. For this reason, the washing effect caused by scrubbing between sand grains is achieved efficiently, and contaminants deposited on or covering a surface of sand grain can effectively be removed.
When the fluidized sand flows upward on a sloped surface of the screw conveyor, the sand gains each having the substantially same hardness scrub each other due to an eddy flow generated there, but the sand grains seldom collide with a member having higher hardness, so that an excessive force is not loaded to the sand grains and there is no possibility that the sand grains are pulverized. Also when the sand grains collide against the internal wall due to the centrifugal force, the sand grains move together with water, so that the energy generated by collision is rather small, and the change for the sand grains to be pulverized is extremely low. Further as there is always water between sand grains scrubbing each other, separated contaminants are dissolved in the cleaning water, and re-deposition due to scrubbing never occurs. For this reason, the sand cleaning effect becomes higher. In the fluidized sand up-flow section, sand grains contact only a top surface of the agitation vane, so that wearing in the agitation member is rather slight.
It should be noted that a clearance between the external edge section of the screw conveyor and the internal wall of the agitation tank should preferably be at least 3 times or more larger than a gain diameter of sand to prevent the sand grains from being pulverized. The fluidized sand flown up to the upper edge opening of the agitation tank is successively sent into the cleaning tank, and is recycled through the lower edge opening into the agitation tank, and also in the cleaning tank and eddy flow is generated and the washing effect because of scrubbing between sand grains is generated also in this tank. Also in the fluidized sand up-flow section, a portion of sand dropped from the external edge section of the screw conveyor again flows upward, so that the washing step by scrubbing becomes longer with the washing effect improved.
In another embodiment of the present invention, a plurality of wing-shaped agitation vanes are provided substantially in parallel to a screw conveyor surface in the sand up-flow section. This agitation vane has a form like a wing, forms a substantially arcuate curved surface, and a plurality of agitation vanes are provided in the rotating direction of the screw conveyor. The fluidized sand flowing along the curved surface of the agitation vane generates a flow of a fluid and then generates an eddy flow. This eddy flow works to further promote the eddy flow generated by the pushing-up effect of the screw conveyor, so that movement of the sand grains to scrub each other is further promoted with the washing effect improved.
A tip of each agitation vane has a sharp or a slight roundish form to prevent the sand gains from being crushed. Taking into consideration the possibility of pulverization of sand grains or increase of load to the agitation vane, an installation angle of each vane is substantially parallel to a surface of the screw conveyor. It is preferable that the agitation vane is fixed to a supporting bar erecting on the surface of the crew conveyor, and also the fluidized sand grains are eccentrically offset along the eternal periphery, it is preferable for the agitation vanes to be provided in this section. For preventing pulverization of sand grains, a round bar is desired as the support bar, but alternately a plurality of vertical and wing-shaped vanes may be provided in the rotating direction of the screw conveyor.
In the fluidized sand up-flow section, the sand grains mainly contact a top surface of the spiral vane and the wing-shaped agitation vane, and the sand grains flow along these sections, so that the agitation member is worn little.